CN108486531B - Preparation method of palladium diselenide two-dimensional crystalline film layer - Google Patents

Abstract

The invention provides a preparation method of a palladium diselenide two-dimensional crystalline film, which comprises the following steps: step 100, preparing a base which takes silicon carbide as a substrate and is provided with a graphene layer on the surface; step 200, keeping the temperature of the base within the growth temperature range of selenium and palladium; step 300, generating selenium atoms and palladium atoms by pure selenium and pure palladium according to a reaction ratio in an evaporation mode, depositing the selenium atoms and the palladium atoms on a base, and reacting the selenium atoms and the palladium atoms on the base to form a two-dimensional ordered crystalline film layer consisting of atoms, wherein the selenium atoms and the palladium atoms are distributed in a selenium-palladium-selenium superposition state in the film layer. The method solves the problem that only a palladium diselenide block body can be obtained in the prior art, can obtain the atomic-level palladium diselenide film layer, and provides convenience for fully utilizing the palladium diselenide to research the physical properties of the palladium diselenide and related devices.

Description

Preparation method of palladium diselenide two-dimensional crystalline film layer

Technical Field

The invention relates to the field of semiconductor preparation, in particular to a preparation method for obtaining a double-layer film structure of palladium diselenide in a two-dimensional crystalline state.

Background

Since 2004, graphene thin films have been discovered and have been the focus of research due to their unique electronic structure and physical properties. The graphene has excellent physical properties such as extremely high electron mobility, high thermal conductivity, high mechanical strength and light transmittance, so that the graphene has an important application prospect in the fields of integrated circuits, gas molecular sensors, supercapacitors, flexible transparent electrodes, terahertz devices and the like. However, since graphene itself has no energy gap, it cannot construct a pn junction like a conventional semiconductor, and thus the application of graphene in the fields of semiconductors and the like is greatly limited.

Based on the excellent characteristics of graphene, the prior art starts to explore, regulate and control other novel two-dimensional film materials. It is composed ofThe transition metal dichalcogenides in (1) are compounds with chemical formula of MX ₂Wherein M represents a transition metal element and X represents a chalcogen element (sulfur, selenium and tellurium). The bulk transition metal dichalcogenide has a layered structure similar to graphene, and the bulk transition metal dichalcogenide contains abundant physical and chemical properties. When it is reduced from bulk by at least several layers or even a single layer, the corresponding physical properties can also vary greatly. For example, molybdenum diselenide can be converted from an indirect bandgap semiconductor to a direct bandgap semiconductor in a single layer, and has a maximum exciton binding energy of 0.55eV, so that the molybdenum diselenide has a wide application prospect in the aspects of semiconductor devices and light-emitting devices.

The palladium diselenide is used as one member of a transition metal disulfide family, and theoretical calculation and transport measurement of the palladium diselenide show that the palladium diselenide has excellent semiconductor performance, higher carrier mobility and on-off ratio, adjustable energy gap, anisotropic transport property, good atmospheric stability and the like, so that the palladium diselenide has wide application potential in the aspects of nano electronics, optoelectronics and the like. However, at present, no mature method for obtaining the thickness of palladium diselenide atomic group can obtain the palladium diselenide thin film only by a tape stripping method, which is inefficient and cannot be widely adopted in industry.

In addition, as a semiconductor two-dimensional material, the controllable modulation of the energy band of the palladium diselenide semiconductor has a very important significance for the application of the semiconductor two-dimensional material, and although theoretical calculation reports that the energy gap of a palladium diselenide bulk material is 0.03eV at present, the experimental verification is not realized, and particularly, the preparation of the palladium diselenide two-dimensional crystalline film has not been reported at all.

Disclosure of Invention

The invention aims to provide a method for artificially and controllably preparing a palladium diselenide atomic-scale thin film layer.

Particularly, the invention provides a preparation method of a palladium diselenide two-dimensional crystalline film layer, which comprises the following steps:

step 100, preparing a base which takes silicon carbide as a substrate and is provided with a graphene layer on the surface;

step 200, keeping the temperature of the base within the growth temperature range of selenium and palladium;

step 300, generating selenium atoms and palladium atoms by pure selenium and pure palladium according to a reaction ratio in an evaporation mode, depositing the selenium atoms and the palladium atoms on a base, and reacting the selenium atoms and the palladium atoms on the base to form a two-dimensional ordered crystalline film layer consisting of atoms, wherein the selenium atoms and the palladium atoms are distributed in a selenium-palladium-selenium superposition state in the film layer.

In one embodiment of the invention, the pure selenium is deposited on the silicon carbide through forming selenium atoms by thermal resistance heating evaporation, and the pure palladium is deposited on the silicon carbide through forming palladium atoms by electron beam heating evaporation.

In one embodiment of the invention, the adding ratio of the pure selenium to the pure palladium is 10-8: 1.

in one embodiment of the present invention, the reaction temperature range is 200-250 ℃.

In one embodiment of the present invention, the semiconductor energy gap of the thin film layer is 1.15 ± 0.07 eV.

In one embodiment of the invention, the base is obtained by processing a 6H-silicon carbide substrate in a vacuum environment; the treatment process comprises the following steps: firstly, 6H-silicon carbide is heated and degassed at 600 ℃, and then heated at 1250-1300 ℃ until a smooth graphene layer is generated on the surface of the 6H-silicon carbide.

In one embodiment of the present invention, the graphene layer on the base includes three states of a mixed graphene layer formed entirely of a single graphene layer, and a double graphene layer formed entirely of a double graphene layer, and a double graphene layer and a single graphene layer combined.

In one embodiment of the invention, when the graphene layer is single-layered, the conduction band bottom and valence band top positions of the grown thin film layer are respectively 0.11eV and-1.04 eV; when the graphene layers are doubled, the positions of the conduction band bottom and the valence band top of the grown thin film layer are respectively 0.31eV and-0.84 eV; when graphene layers are mixed, thin film layers continuously grow across the layers, and pn junctions are formed in the thin film layers at the cross regions.

The method solves the problem that only a palladium diselenide block body can be obtained in the prior art, can obtain the atomic-level palladium diselenide film layer, and provides convenience for fully utilizing the palladium diselenide to research the physical properties of the palladium diselenide and related devices.

Drawings

FIG. 1 is a schematic flow diagram of a method of making one embodiment of the present invention;

FIG. 2 is a schematic diagram showing the comparison of the energy gap positions after the palladium diselenide thin film layer is formed by using single and double graphene layers;

fig. 3 is a schematic diagram of the structure and energy band structure of the palladium diselenide thin film layer generated by adopting a single-double graphene layer mixed structure.

Detailed Description

As shown in fig. 1, the method for preparing a palladium diselenide two-dimensional crystalline thin film layer according to an embodiment of the present invention generally includes the following steps:

step 100, preparing a base which takes silicon carbide as a substrate and is provided with a graphene layer on the surface;

the base is obtained by processing a 6H-silicon carbide substrate in a vacuum environment; except the appointed graphene layer which needs to be obtained, the generated graphene layer needs to be leveled, and the specific treatment process comprises the following steps: firstly, 6H-silicon carbide is heated and degassed at 600 ℃, and then is repeatedly heated at 1250-.

Step 200, keeping the temperature of the base within the growth temperature range of selenium and palladium;

it has been found through experimentation that selenium and palladium do not react at any temperature or that the reaction product is in the form of a thin film of atomic layers, and therefore the temperature at which they react is controlled, which is present on the susceptor, i.e., selenium and palladium can form the desired product on their surfaces as long as the susceptor is maintained within a specified temperature range. The reaction temperature range for selenium and palladium in this embodiment is 200-250 ℃.

The temperature maintaining mode of the base can be a heating table or a direct electric heating mode, and the heating time and the temperature can be conveniently controlled.

Step 300, generating selenium atoms and palladium atoms by pure selenium and pure palladium according to a reaction ratio in an evaporation mode, depositing the selenium atoms and the palladium atoms on a base, and reacting the selenium atoms and the palladium atoms on the base to form a two-dimensional ordered crystalline film layer consisting of atoms, wherein the selenium atoms and the palladium atoms are distributed in a selenium-palladium-selenium superposition state in the film layer.

In the experiment, raw materials with high purity are stored as much as possible, for example, the purity of selenium and palladium is not less than 95% in the embodiment.

In addition, in order to obtain an expected palladium diselenide atomic layer thin film material, the adding proportion of selenium and palladium needs to be controlled, the proportion is determined according to the atomic number of the combined palladium diselenide atomic layer thin film material and is generally 3 times larger than the proportion of the combined palladium diselenide atomic layer thin film material, so that sufficient reaction can be guaranteed, and the adding proportion of specific selenium and palladium can be 10-8: about 1.

When the material is put into the reactor, pure selenium can be heated and evaporated by a thermal resistance mode to form selenium atoms, so that the generated selenium atoms are deposited on the silicon carbide, and pure palladium can be heated and evaporated by an electron beam to form palladium atoms, so that the generated palladium atoms are deposited on the silicon carbide. The deposited selenium atoms and palladium atoms can react to generate an atomic-scale thin film layer under the action of the base temperature and the surface graphene thereof.

As shown in the figure, selenium atoms and palladium atoms in the film layer form palladium diselenide in a selenium-palladium-selenium superposition combination mode, and the palladium diselenide mutually forms an atomic-level selenium-palladium-selenium three-layer superposed film layer on the surface of the graphene layer in a two-dimensional ordered crystalline structure.

The results of the thin film layer detection by the scanning tunnel microscope are as follows:

the thin film layer is a smooth and flat thin film, and the distance between the thin film and the substrate is 0.78 nm. And the selenium atom arrangement of the topmost layer in the selenium-palladium-selenium structure and the in-plane period of the two-dimensional periodic structure are 0.59nm multiplied by 0.60nm, and the parameters are consistent with the parameters of the bulk structure of palladium diselenide.

In addition, the energy gap of palladium diselenide of the bulk material is only 0.03eV (obtained by calculation), while the energy gap of the semiconductor of the platinum diselenide film layer obtained by the method is 1.15 +/-0.07 eV, so that the energy gap of the palladium diselenide film layer is obviously increased after the palladium diselenide film layer is made into a film structure, and the size of the energy gap is an important parameter index for a semiconductor material, thereby having a decisive influence on the performance of a semiconductor device and a photoelectric device thereof. Specifically, a band gap of 1.15 ± 0.07 corresponds to a visible light band, so that it can be widely used in the field of photocatalysis.

The selection of the substrate, the beam current ratio and the growth temperature determines the Molecular Beam Epitaxy (MBE) growth of the final palladium diselenide thin film layer, and in the embodiment, if the materials forming the substrate are different, or the beam current ratio of selenium and palladium is too small, or the temperature of the substrate cannot be controlled within a set temperature range, the substrate can affect whether the palladium diselenide crystalline thin film layer can be successfully prepared.

According to the embodiment, the current situation that only a palladium diselenide block can be obtained in the prior art is solved through the method, the atomic-level palladium diselenide film layer can be obtained, and convenience is provided for researching physical properties of palladium diselenide and related devices by fully utilizing the palladium diselenide.

As shown in fig. 2 and 3, in an embodiment of the present invention, the number of graphene layers is set, so that the electronic volt values at the conduction band bottom and valence band top of the generated palladium diselenide thin film layer can be changed, and the graphene layer on the base in the preparation process can be divided into three cases, i.e., one case is completely formed by a single graphene layer; secondly, the graphene layer is completely formed by double graphene layers; and thirdly, forming a mixed graphene layer by combining the double-layer graphene layer and the single-layer graphene layer.

Under the three states, the energy band size of the generated platinum diselenide film layer is not changed and is 1.15 +/-0.07 eV, but the energy gap position is changed; the description is as follows:

when the graphene layer is single-layered, the positions of the conduction band bottom and the valence band top of the grown thin film layer are respectively 0.11eV and-1.04 eV; when the graphene layers are doubled, the positions of the conduction band bottom and the valence band top of the grown thin film layer are respectively 0.31eV and-0.84 eV; when graphene layers are mixed, thin film layers continuously grow across the layers, and pn junctions are formed in the thin film layers at the cross regions.

Compared with a palladium diselenide thin film layer generated on a double-layer graphene layer, the energy gap of the palladium diselenide thin film layer on the single-layer graphene layer is doped with 0.2eV by electrons, the difference is caused by the electron doping effect of the single-layer graphene layer on the silicon carbide on the palladium diselenide thin film layer, so that the position change of an internal energy band of the generated continuous thin film layer is caused by the difference of the substrate, namely the number of the graphene layers on the substrate can be changed, the adjustability of the energy band of the palladium diselenide thin film layer is further realized, and the controllable modulation of the semiconductor energy gap has important significance for the application of devices. More importantly, the palladium diselenide thin film layer can be continuously grown across the mixed region of the substrate single-double graphene layer, so that the in-plane pn junction of the palladium diselenide thin film layer is realized to a certain extent, which is always concerned, and the possibility is provided for future semiconductor device and logic circuit application.

Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.

Claims (6)

1. A preparation method of a palladium diselenide two-dimensional crystalline film layer is characterized by comprising the following steps:

step 100, preparing a base which takes silicon carbide as a substrate and is provided with a graphene layer on the surface;

step 200, keeping the temperature of the base within the growth temperature range of selenium and palladium;

300, generating selenium atoms and palladium atoms by pure selenium and pure palladium according to a reaction ratio in an evaporation mode, depositing the selenium atoms and the palladium atoms on a base, and reacting the selenium atoms and the palladium atoms on the base to form a two-dimensional ordered crystalline film layer consisting of atoms, wherein the selenium atoms and the palladium atoms are distributed in a selenium-palladium-selenium superposition state in the film layer;

the pure selenium is formed by thermal resistance type heating evaporation to form selenium atoms to be deposited on the silicon carbide, and the pure palladium is formed by electron beam heating evaporation to form palladium atoms to be deposited on the silicon carbide;

the adding proportion of the pure selenium to the pure palladium is 10-8: 1.

2. the production method according to claim 1,

the reaction temperature range is 200-250 ℃.

3. The production method according to claim 1,

the semiconductor energy gap of the thin film layer is 1.15 +/-0.07 eV.

4. The production method according to claim 1,

the base is obtained by processing a 6H-silicon carbide substrate in a vacuum environment; the treatment process comprises the following steps: firstly, 6H-silicon carbide is heated and degassed at 600 ℃, and then heated at 1250-1300 ℃ until a smooth graphene layer is generated on the surface of the 6H-silicon carbide.

5. The production method according to claim 4,

the graphene layer on the base comprises three states of a mixed graphene layer formed by completely forming a single-layer graphene layer and a double-layer graphene layer and combining the double-layer graphene layer and the single-layer graphene layer.

6. The production method according to claim 5,

when the graphene layer is single-layered, the positions of the conduction band bottom and the valence band top of the grown thin film layer are respectively 0.11eV and-1.04 eV; when the graphene layers are doubled, the positions of the conduction band bottom and the valence band top of the grown thin film layer are respectively 0.31eV and-0.84 eV; when graphene layers are mixed, thin film layers continuously grow across the layers, and pn junctions are formed in the thin film layers at the cross regions.

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